For crop sensor, Tamorn 17-50 2.8 first, then 70-200 4L (IS if you can afford it), but I'm thrilled with my 70-200 4L non-IS for under $600.00. If you shoot sports, it may be too slow, but for outdoor candids at festivals and family picnics, and outdoor portraits, the 70-200 4L kicks butt IQ wise for a very reasonable cost.
And for $80.00 you won't find a better portrait lens for a crop body than the nifty fifty! IQ rocks, build quality sucks. Sharpest lens I own!